Electrostatic powder sprayer



Dec. 13, 1966 w. G. BUHLER 3,292,045

ELECTROSTATIC POWDER SPRAYER Filed April 23, 1964 6 Sheets-Sheet l j MQ,M Z7 "WMLLW Dec. 13, 1966 w. G. BUHLER 3,292,045

ELEoTRosTATIc POWDER SPRAYER Filed April 2:5, 1964 e sheets-sheet 2INVENTOR. A44/Gef 6. Ja//Af Dec. 13, 1966 w. G. BUHLER 3,292,045

lELEGTROSTTIG POWDER SPRAYER Filed April 23, 1964 6 Sheets-Sheet 5 BYW7, @Md/xxx@ Dec- 13, 1966 w. G. BUHLER ELECTROSTATIC POWDER SPRAYBR 6Sheets-Sheet 4 Filed April 25, 1964 lINVENTOR.

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lLllllll Il W. G. BUHLER ELECTROSTATIC POWDER SPRAYER Dec. 13, 1966 v 6Sheets-Sheet 5 Filed April 23, 1964 oovowwowsrol Q33? o VAYO . INVENTOR,fraz/P51 6. Ms/5? Dec; 13, 1966 w. G. BUHLER 3,292,045

ELECTROSTATIC POWDER SPRAYER Filed April 23, 1964 6 sheets-smet 6 UnitedStates Patent ce 3,292,945 Patented Dec. 13, 1966 3,292,045ELECTROSTATIC POWDER SPRAYER Warren G. Buhler, Westfield, NJ., assignorto OXY-Dry Sprayer Corporation, New York, N.Y., a body corporate of NewYork Filed Apr. 23, 1964, Ser. No. 362,106 3 Claims. (Cl. 317-3) Thisinvention relates to electrostatic powder sprayers, and moreparticularly to powder sprayers capable of laying down a substantiallyuniform layer of ne powder material.

The prior electrostatic powder sprayers have usually included 1a :powderbox, la metering mechanism for dispensing powder material from thepowder box at a substantially uniform rate, and apparatus for providingan electrostaic field to free powder particles from the meteringmechanism 4and to disperse the powder particles. Typically, theelectrostatic iield would be created by a single gas filled dischargetube secured in a fixed position relative to the metering mechan-ism.Substantial success has been -achieved with these prior units whendesigned to dispense a particular type of powder material with Ialimited range -of dispensingrates.

An object -of this invention is to provide an electrostatic powdersprayer capable of dispensing a wide variety of powder materials withoutany signilicant limitation upon the available dispensing rates.

Another object yof the invention is to provide a powder sprayer which isadjustable so as to vary they field pattern and strength of theelectrostatic eld used to free the powder particles from the meteringmechanism and to disperse the powder particles.

Still yanother `object is to provide an electrostatic powder sprayerwhich can be adjusted to provide symmetrical or non-symmetricalelectrostatic field so as to control the downward direction `of fallingpowder particles.

Another object is to provide an electrostatic powder sprayer wherein thedischarge tubes utilized to create the electrostatic field aredetachably secured and easily replaced.

The Amanner in which the 'foregoing and other objects are achieved isset forth more fully in the following specication which describes a fewillustrative embodiments within the scope of this invention. Thedrawings form a part -of this specification wherein:

FIG. 1 is a perspective view, with portions broken away, illustratingone end of the powder sprayer;

FIG. 2 is a perspective view illustrating the other end of the powdersprayer with the journal structure partially disassembled;

FIG. 3 is a plan view of the powder sprayer and associated drivingmechanism;

FIG. 4 is a side view of the powder sprayer;

FIG. 5 is an end view -of the powder sprayer taken along line 5 5 asindicated in FIG. 4;

FIG. 6 is a cross sectional view of the powder sprayer taken along line6 6 `as indicated in FIG. 4:

FIG; 7 is :a longitudinal cross sectional view of the powder sprayerillustrating the journal structure and taken along line 7 7 as indicatedin FIG. 3;

FIG. 8 is an enlarged partial cross sectional view of the structureshown in FIG. 6 illustrating the details of the wiping blade assembly;

FIG. 9 is an illustration of the roller surface in accordance with oneembodiment of the invention as seen from line 9 9 in FIG. 8;

FIG. 10 is an illustration -of an Ialternative surface structure for theroller as seen along line 9 9 in FIG. 8;

FIG. 11 is a cross sectional view illustrating the socket structure forretaining one end of a discharge tube; and

FIGS. 12 and 13 are cross sectional views of one of the end bracketstaken along line 12-12 in FIG. 4 and illustrating the adjustabledischarge tube support structure.

GENERAL DE'scRrPrroN The powder sprayer in accordance with thisinvention includes la dispensing roller and a pair of wiping bladeswhich tangentially engage the dispensing roller on opposite sides. Asthe r-oller rotates, powder is dispensed at a substantially uniform ratefrom a powder box llocated above the dispensing roller. A separateelectrostatic discharge tube is positionable beneath each of the wipingblades. Each of these discharge tubes is detachably secured bet-Ween aspring biased socket at one end and :a rigid socket at the other end. Adischarge tube is inserted by first forcing one end into the springbiased socket, thereby compressing a spring within the socket, and bythereafter releasing the discharge tube so that the `other end isretained in the rigid socket by means of spring pressure. The dischargetube is easily removed by moving the tube longitudinally to `againcompress the spring, and by then removing the discharge tube from theThe end portions Iof the receptacle forming the powder box areconstructed to provide arcuate surfaces which are eccentric with respectto the cylindrical surface of the dispensing roller. A pair of arcuatesupport brackets are attached to slidably engage these arcuate surfacesland are constructed to provide pivotable support for the sockets whichengage the ends of the discharge tubes. Thus, the discharge ltubes canbe placed in virtually any desired position parallel to the dispensingroller because of the double adjustments achieved by means of thepivotable and slidable support structure. By varying the position of thedischarge tubes, the eletrostatic field pattern and the strength of theelectrostatic field can be vari-ed as desired. As 1a result, theelectrostatic powder sprayer can be :adjusted for a wide variety ofpowder materials and -operating conditions.

POWDER BOX, WIPER BLADES AND AIR CURTAIN First, referring to FIGS. 1-13,an ladvantageous embodiment of the invention is illustrated wherein thepowder sprayer includes a powder box 1, defined by a pair of spacedapart side panels 2 and 3, end brackets 4 and 5 and a dispensing roller11. The side panels are secured between the end brackets by means of twopairs of support blocks 9 and 10, these support blocks being formed asan integral portion of the end brackets. The side panels :are secured tothe support blocks by means of suitable screws as illustrated. A spacermember 12 is secured intermediate the ends of `the side panels and isflush with the upper edge thereof. A lid 6 is secured to the upper edgeof side panel 2 by means of a hinge 9 and i-s dimensioned t-o cover thetop of the powder box and wrap over the upper edge of side panel 3 whenin the closed position. Dispensing roller 11 is journaled in the endbrackets .and is disposed between the lower edges of side panels 2 and3.

The side panels, best seen in FIGS. l, 6 and 8, are preferably integralextruded aluminum panels. Side panel 3 includes a vertical outer portion14, a sloping portion 15 and a lower horizontal portion 16, whichportions define a plenum chamber 17 having a generally triangular crosssection and extending through the side panel from end to end. Thesloping surface 15 lies in a plane tangential to dispensing roller 11and meets vertical portion 13 somewhat below the upper edge of the sidepanel. Surface 15 extends beyond the horizontal portion 16 and forms onesurface of a lower extended portion 18. The other flat surface ofextended portion 18 is a blade retaining surface 19 which lies in aplane which meets the plane of surface 15 at the point of tangency withthe roller, or somewhat below the point of tangency. The right dihedralangle between these planes is approximately 20 degrees. The lower edgeof extended portion 13 is rounded as shown.

A longitudinal V-shaped groove 25, best seen in FIG. 8, is machined intothe lower surface of horizontal portion 16. This groove forms an outervertical groove surface 26 and inwardly sloping groove surface 27.Preferably, the groove is located directly below the outer portion ofplenum chamber 17. A plurality of holes 28 are drilled through bottomportion 16 extending between the apex of groove 25 and plenum chamber17.

When the side panel is secured in position, end bracket 4 seals off oneend of plenum chamber 17, and end bracket seals ofl the other end. Ahose connecting nipple 29 is threaded into a threaded bore 30 passingthrough end bracket 4 so as to communicate with plenum chamber 17. Asuitable air pump can be coupled to the plenum chamber Via an air hose(not shown) to create a pneumatic pressure within the chamber. As aresult, a plurality of air jets are formed via holes 28. Because ofgroove 25, these jets tend to fan out elliptically and thus provide arelatively uniform air curtain extending between adjacent holesthroughout the entire length of the side panel. Due to sloping groovesurface 27, a portion of each of these jets is directed inwardly toprevent accumulation of powder on retaining member 20, adjusting screws22 and wiping blade 23 located beneath the side panel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, the bracket 4 seals off one end of Aplenum chamber 17,and end bracket 5 seals off the other end. Preferably, a sealing gasketis cemented in position between the end brackets and the side panels. Ahose connecting nipple 29 is threaded into a threaded bore 30 passingthrough end bracket 4 so as to communicate with plenum chamber 17. Asuitable air pump can be coupled to the plenuml chamber via an air hose(not shown) to create a pneumatic pressure within the chamber. As aresult, a plurality of air jets are formed via holes 28. Because ofgroove 25, these jets tend to fan out elliptically and thus provide arelatively uniform air curtain extending between adjacent holesthroughout the entire length of the side panel. Due to sloping groovesurface 27, a portion of each of these jets is directed inwardly toprevent accumulation of powder on retaining member 20, adjusting screws22 and wiping blade 23 located beneath the side panel.

Side panel 2 is identical to side panel 3 and includes components 33-49corresponding, respectively, to components 13-29 of side panel 3. Asshown in FIG. 6, v

the powder material to be dispensed is placed in the powder box betweensloping surfaces 15 and 35 and above dispensing roller 11. Thus, thesloping surfaces serve to funnel the powder downwardly toward thedispensing roller. It should be noted that the plenum chambers aretherefore located in an area which would otherwise be wasted space.Plenum chambers 17 and 37 are suiciently large so that the air pressuretherein is substantially uniform over the entire length of the sidepanels.

Wiping blades 23 and 43 are each constructed from a thin, flexible stripof blue spring steel and are preferably coated with a fluorocarbonmaterial. These blades are approximately one inch wide and have a lengthequal to the length of side panels 2 and 3. Holes are drilled throughthe blade near the upper edge and are spaced on two inch centers.

Semi-rigid retaining member 20, best seen in FIG. 8, is preferably anextruded aluminum strip equal in length to wiping blade 23 and sidepanel 3. Longitudinally spaced holes are drilled through retainingmember 20 corresponding in position to the holes in blade 23, and

corresponding tapped holes are drilled into extended portion 18 of sidepanel 3, these holes being normal to blade retaining surface 19. Wipingblade 23 is positioned between extended portion 18 of the side panel andretaining member 20, and this assembly is secured by means of suitableround head adjusting screws 22. Preferably, the holes in the wipingblade, retaining member and extended portion of the side panel areaccurately aligned so that the wiping blade can easily be replaced.

Retaining member 20 includes a flat blade engaging surface which curvesinto an inwardly extending rib 21 at the lower edge thereof. Thedistance between screw 22 and rib 21 must be greater than the distancebetween screw 22 and the lower edge of extended portion 18. The distancebetween screw 22 and the upper edge 24 of the retaining member ispreferably somewhat greater than the distance along surface 19 betweenscrew 22 and the lower surface of bottom portion 16. Thus, when screw 22is tightened, moving retaining member 20 toward retaining surface 19,the upper edge 24 strikes the lower surface of bottom portion 16.Thereafter, when screw 22 is further tightened, retaining member 24pivots about edge 24 and applies pressure along the longitudinal centerline of blade 23 via rib 21. As a result, the blade is bent inwardly byrib 21 along the center line of the wiping blade which is locatedbetween extended portion 18 and line of tangency on roller 11. Thus, thewiping blade is laterally deformed and takes on an S-shaped bend asshown in FIG. 8. In this manner, the exible blade becomes rigid andsubstantially straight in the longitudinal direction. Each of the screws22 are separately adjustable, and hence, the pressure applied by thewiping blade against dispensing roller 11 can be adjusted as desired atselected points along the blade. This permits adjustments to compensatefor uneven wear or for tolerances in the dispensing roller surface orthe side panel. Also, it is possible to adjust the blade so that greaterpressure is exerted against the dispensing roller in selected areas tothereby obtain a non-uniform dispensing rate when desired.

END BRACKETS AND DISCHARGE TUBE MOUNTING STRUCTURE End brackets 4 and 5are identical to one another and are secured abutting the ends -of sidepanels 2 and 3 by l.means of support blocks 9 and `10 respectively whichform inte-gral portions of the end brackets. The end brackets thus serveas closure members for the ends of the powder box and the en-ds of theplenum chambers within the side panels. Also, the end brackets supportbearings .for the journals `for dispensing roller 11, arcuate surfacesfor cooperating with the discharge tube supporting structure, andbracket portions 4for securing the powder sprayer to associatedapparat-us or a suitable support frame structure.

End bracket 4 is an integral structure including an end closure membery60, a substantial circular boss 61 extending horizontally away Afromthe -surface of closure member, and a support leg `62 extendinghorizontally from the flat sunface of the boss. The diameter of circularboss 61 is approximately equal to the distance between the outersurfaces of side walls 2 and 3. Boss 61 is positioned to acco'mrnodatean off-center journal housing 63 for dischange roller 11, the dischargeroller being located -as Ishown Iin FIG. 12. The lower portion ofclosure member 60, i.e., the portion lying below the horizontal centerline of boss 61, is curved and conforms to the circular configuration`of the boss. Support blocks 9 are secured to the edges lof closuremember 60 and extend in the direction of the side panels. Support blocks9 are spaced apart so that they will lie Ion the outer surfaces `of theside panels when the end bracket is secured in position. The upper edges`of closure member 60 and boss 61 are flush with the upper edges -ofsi-de panels 2 and 3.

Support leg `62. can have any desired coniiguration and includes a pairof slots 64 and 65 therein extending through the support leg from top tobottom. A-s shown in FIG. 7, support leg `62 is positioned slightlybelow the upper surface of boss 61 and is strengthened by means of `atapered rib 66 extending from boss 61 along the upper surface olf thesupport leg. The support leg can be either horizontal as shown, or canbe vertical to facilitate side mounting.

End support bracket 5 is an integral structure identical to end supportbracket 4 and includes an end closure member 70, a substantiallycircular boss 71, a pair of spaced apart support blocks 10, and asupport leg 72 with an associated strengthening ri-b 76 and slots 74 and75. Thus, when ,the end brackets are secured in the positions as shownin FIGS. 1 and 2,A the brackets close the ends of the powder lbox andlalso close the ends of the plenum chambers within the si-de panels.Preferably a sealing gasket is cemented in position between the endbrackets and the ends of the side panels. As previously mentioned, apair of bores 30 and 50 are provided extending th-rough end bracket 4and are each positioned to communicate with a different one of theplenum chambers 17 and 37 respectively. The threa-ded bores are adaptedto accommodate threaded hose connecting nipples 29 and 39 respectively.End bracket 5 likewise includes a pair of threaded bores so that thisend bracket will be identical to end bracket 4. The threaded bores inend bracket 5, howeve-r, are lnot used and are therefore sealed -bymeans of suitable threaded plugs 77 and 78. The 4assembled powdersprayer can be positioned as desired by mea-ns of suitable bracketmembers (not sh-own) bolted to support legs 62 and 72 or by bolting thesupport legs directly to a sui-table supporting structure.

Discharge tubes 80 and 81 are similarly constructed a-nd each include acylindrical glass tube which is evacuated and then lled with an inertrgas .such as argon. The glass tubes are slightly l-onger than the sidepanels and are internally coated with a suitable phosphorous material.The discharge tubes include a cathode at one end only. As shown in FIG.1l, the cathode end of the discharge tube includes a cup shaped cathodemember S2 connected to a conductive metallic end cap 83 by means of asuitable support condu-ctor 84.

It is `desirable that the .discharge tubes be positioned generallyparallel to dispensing roller 11 and that they be adjustable in positionwith respect to the roller. Also, it is desirable tha-t the tubes bedetachably 'secured so that they can easily be replaced.

The -dischange tube support structure yfor tube 81 includes a supportarm 90 having an arcuate inner surface with the same radius of curvatureas the arcuate surface 91 at the periphery of boss 61. Thus, the innersurface of support arm 90 is adapted to engage arcuate surface 91 asshow-n in FIG. 1, and is adjustatble with respect to the boss. Supportarm 90 includes an elongated locking slot 92 including an elongatedannular shoulder 93 (best seen in FIGS. l2 and 13) which is concentricwith the arcuate surface `of boss 61. A tapped hole is bored into boss61 along the horizontal center line and is dimensioned to accommodate asocket type cap screw 94 which passes through slot 92. Thus, when cap.screw 94 is loosely placed in position, -support arm 90 can slide froman upper position as shown in FIG. l2 to a lower position shown in FIG.13. It should be noted that arcuate surface 91 is eccentric with respectto the dispensing roller surface due to the |off-center locati-on of thejournal housing with respect to boss 61. Support aum 90 can be rigidlysecure at any position by tightening cap screw 94 so that the head ofthe screw engages shoulder 93 of the locking slot.

The lower porti-on of support `arm 90 (as viewed in FIG. 1) is offsetand is constructed to provide a bifurcated end portion 95 dimensioned-to accommodate a tab 96 extending from a spring lbiased 4tube socket97. As .shown in FIG. 11, a pair of axially aligned threaded aperturespas-s through the leg portions of bifurcated end 95 and a smallerdiameter, axially aligned, aperture passes through tab 96. A pair ofsocket type, headless, set screws 98 and 99 are threaded into the legportions of bifurcated end so that the dog point ends of the .set screwsreside within the aperture passing through tab 96. In this manner,socket 97 is pivotably secured to support arm 90 (as illustrated in FIG.13) and can be rigidly maintained in any desired pivoted position byappropriate adjustment of set .screws 98 and 99.

A support arm `100, which is a mirror image of support arm 90, isadapted to engage the arcuate surface 101 located at the periphery ofboss 71 of end bracket 5. Su' port arm is secured to end bracket 5 bymeans of a cap screw 104 which passes through an elongated locking slot102 and engages .shoulder 103 within the slot. A tab 106 extending 'froma cup shaped tube .socket 10.7 is pivotably secured to support .arm 100by means of an olfset bifurcated end portion 105. Tube socket 107 ispreferably constructed :from a material having a high electricalresistance and is dimensioned internally to accommodate the end ofelectrostatic tube 81.

Spring biased socket 97 includes a generally cylindrical outer housing110 which is partially closed at one end. An insulated conductor 111passes through the partially closed end of housing 110 and through thecenter of a retaining washer 112. The free end of the conductor isembedded in a globule or bead of solder 113 to provide a relativelylarge conductive surface and to prevent conductor 111 from pulling outof the washer. A spring 114 is disposed between retaining washer 112 andthe partially closed end portion -of housing 110 to urge the retainingwasher away from the partially closed end of the housing. As previouslymentioned, tab 96, which extends radially from housing 110, is pivotablysecured bythe bifurcated end portion of support arm 901. Housing 110 ispreferably an integral structure constructed from a material having ahigh electrical resistance.

Conductor 111 after emerging from the end of socket 97, is connected toone end of a high voltage secondary winding 115 of a transformer 116,the other end of the secondary winding being connected to a suitableground, which may be the side panels of the powder sprayer or a groundsurface located at some point below the sprayer. Primary winding 117 oftransformer 116 is connected to a suitable 60 cycle alternating currentsource. Transformer 116 is preferably constructed to provideapproximately 10,000 volts to electrode S2 via conductor 111.

Discharge tube 81 is installed by inserting the electrode end intospring biased socket 97 thereby compressing spring 114. The other end ofthe discharge tube is then inserted into socket 107, and when released,is retained in socket 107 by virtue of the force extended by spring 114.Thereafter, discharge tube 81 can easily be adj-usted to any desiredposition parallel to dispensing roller 11 by means of the pivotableconnection between the sockets and support arms 90 and 100, or byadjusting the position of the support arms relative to end brackets 4and 5.

The adjustable supportl structure for discharge tube 80 is essentiallythe same as the supporting structure for discharge tube 81, except thatit is attached to position tube `80 on the opposite side of dispensingroller 11. The components comprising the adjustable supporting structurefor discharge tube 80 are designated with reference numerals 1Z0-144corresponding respectively to reference numerals 90-114. Conductor 141emerging from socket 127 is also connected to the ungrounded end ofsecondary winding 115 (FIG. 11).

ROLLER ASSEMBLY Roller 11 can be a solid steel roller with longitudinalextending shafts, as shown in the drawings, or can include a hollowcylindrical roller with suitable roller gudgeons secured to the ends toform the longitudinal extending shaft portions. The length of the rollerportion is slightly less than the distance between end brackets 4 and 5as determined by the length of the side panels.

Journal shaft 150, extending from one end of roller 11, passes through ajournal opening 151 in end bracket 5 forming part of journal housing 73,and through a flanged bearing 152 constructed from a suitable bearingmaterial, preferably a fluoro-carbon material. Journal opening 151 isdimensioned to accommodate flanged bearing 152 and includes an annularrecess dimensioned to seat the flange of the bearing. As shown in FIG.2, flanged bearing 152 is slid into position from outside end bracket 5and is thereafter secured to the end bracket by means of set .screws 153passing through the ange of the bearing. An annular recess is alsoprovided on the inner side of end bracket 5 surrounding journal opening1'51, to accommodate a felt washer 154 which provides a jou-rnal sealand prevents powder from entering the bearing structure. A collar 155 isslid over the end of shaft 150 and is rigidly secured to the shaft bymeans of a set screw 156. This collar is positioned adjacent bearing 152and prevents longitudinal movement of the roller with respect to the endbracket. A sprocket gear 157 is secured near the end of shaft 150 bymeans of a suitable set screw passing through the hub of the gear. Asshown in FIG. 3, a chain 158 couples sprocket gear 157 to an associatedlsprocket gear mounted on the shaft of an electric motor 159. Motor 159is preferably of a va-riable speed drive type capable of rotating roller11 at speeds ranging from small fractions of one `r.p.m. to Iiftyr.p.rn.

Journal 63 in end bracket 4 is similar to journal 73 previouslydescribed and incudes a flanged bearing 162 secured in a journal opening161 by mean-s of set screws 163 so that the bearing surrounds shaft 160extending longitudinally from the end of roller 11. A felt sealingwasher 164 is provided surrounding the shaft on the inner side of endbracket 4, and a collar 165 is secured to shaft 160 adjacent bearing 162by means of set screws 166.

The cylindrical surface 170 of roller 11 is advantageously coated with aliuoro-carbo-n material and thereafter further processed to provide apowder receptive surface. The process surface of the roller isillustrated in a. magnified view of the roller surface shown in FIG. 9and `includes an almost infinite number of powder carrying cavities. Asillustrated in FIG. 8, the powder material in powder box 1 is fed bygravity into the area between roller 11 and wiping blade 23. As theroller rotates, a thin layer of powder wedges past the wiping blade. Thethickness of the powder layer, and hence, the quantity of powderdispensed, depends on the adjustment of screws 22, which in turndetermines the blade pressure against the roller. The minimum rate atwhich powder can be dispensed is determined by the capacity of thepowder carrying cavities and the minimum rotation speed of thedispensing roller. The dispensing rate can be increased by eitherincreasing the rotation speed of the roller or by decreasing the bladepressure against the surface of the dispensing roller.

An alternative surface structure for the dispensing roller isillustrated in FIG. l0 where the cylindrical surface is engraved topresent a uniform waffle-like pattern. This structure increases thecapacity of the powder carrying cavities which is desirable where highdispensing rates are required or large powder particles are beingdi-spensed. Preferably, the engraved dispensing roller is coated with afluorocarbon material. With the dispensing roller surface shown in FIG.10, the dispensing rate can also be varied by adjusting the speed ofrotation for the dispensing roller and the wiping blade pressure.

Although it has been mentioned that the dispensing rate for a givenroller surface can be adjusted by varying the 4roller speed and bladepressure, there is a practical limit to these adjustments sinceeventually the powder will begin to sift, that is, the powder will beginto come through in uneven chunksresulting in an uneven and relativelyuncontrolled powder distribution. The maximum dispensing rate for aparticular roller varies in accordance with the type of powder beingdispensed. When a particular roller does not achieve the desireddispensing rate, the roller is replaced with another roller havinglarger powder carrying cavities.

It is significant that the roller `and the wiping blades are coated witha iluorocarbon material and that the roller bearings are likewiseconstructed from a iluorocarbon material. The iluorocarbon material usedfor coating the roller and wiping blades is preferably the polymer oftriuorochloroethylene such as marketed under the brand name Kel-F andcharacterized by the formula (CF2-CFCl)x. First, these -materialsexhibit a high chemical resistance so that other material, such as thepowder being dispensed, cannot readily adhere to the roller and wipingblade surfaces. Second, tluorocarbon materials have substantially a zeromoisture absorption characteristic and therefore reduce the possibilityof moisture contamination of the powder being dispensed. Third, thesematerials have a relatively high compression strength and hence,excellent wear characteristics. This is significant in the bearings, andalso with respect to the roller and wiping blade arrangement which issubjected to the constant rubbing action as the powder material, whichmay be abrasive, passes between the roller and wiping blade. Further,uorocarbon materials have a high electric resistance and high resistanceto electrostatic charges. It should be noted that the steel roller, dueto the flanged fluorocarbon bearing and iluorocarbon coating iselectrically isolated and hence, is electrically insulated from theelectrostatic lfield. If the dispensing rolle-r were not isolated, therewould be same electric charge, from the electrostatic field created bydischarge tubes Si) and 81, which would be carried into the powder boxby means of the roller and thereby electrostatically contaminate thepowder material. This electrostatic contamination would adversely effectthe dispensing of the powder material.

ASSEMBLY AND OPERATION The powder sprayer in accordance with thisinvention is of a generally symmetrical design so as to minimize thenumber of different components. The side panel and wiping blade assemblyon one side of the roller is identical to the side panel and wipingblade assembly on the other side. The end lbrackets are identical to oneanother, and the two discharge tubes supporting structures are alsosubstantially identical. This symmetrical construction in alsoadvantageous since the dispensing roller can be rotated in eitherdirection and'the entire unit can Ibe installed with either side panelfacing outwardly.

The powder sprayer is installedwith the dispensing roller positionedhorizontally, usually less than a foot above the surface to be coatedwith the powder material. Usually, the powder receiving surface is inthe form of a moving web or sheet.

The powder or dusting material to be dispensed is either placed directlyin the powder box above dispensing roller 11 or is supplied by asuitable feed mechanism. Thereafter, the drive motor is energized torotate motor 11. The roller, if rotating in a clockwise direction,forces powder past wiping blade 23, in which case wiping blade 43 actsas a `seal between the side :panel and the other side of the roller. Onthe other hand, if the dispensing roller -rotates in a counter-clockwisedirection, wiping blade 43 provides the metering function and wipingblade 23 acts as the seal. In either event, the powder material ismetered out at a uniform rate. Thereafter, the force of `gravity and theforce created by the electrostatic fiel-d pro- |vided by the dischargetubes, strips the roller clean so that the powder material falls to thesurface below.

When discharge tubes and 81 are ener-gized, potential gradients arecreated surrounding the tubes which in turn ionize some of the airmolecules in the vicinity of the discharge tu'be. This eifect is knownas corona. The ionized particles having the same polarity as th-atappearing in the surface of the discharge tube stream away from theIdischarge tubes creating air currents referred to as electronic winds.These electronic winds are in a .generally downward direction in thearea beneath dispensing r-oller 11. The downwardly directed electronicwind and the electr-ostatic attraction of the powder particles, assistthe forces of gravity in removing the particles from the roller. A largenumber of the released particles become charged with the same polarityas the surrounding air molecules. This effect creates a powder cloudbeneath the dispensing roller and brings about a more uniform dispersionof powder particles than could otherwise be achieved.

As previously mentioned, the dispensing rate is determined by therotational speed of dispensing roller 11, and the blade pressure againstthe dispensing roller surface. -It should be noted that the wiping bladeis relatively narrow and that the retaining member, which controls theblade pressure, is relatively close to the dispensing roller. With thisarrangement the blade pressure can 'be controlled with considerableaccuracy. Furthermore, since the adjusting screws are individuallyadjustable, the blade pressure can be adjusted separately in diierentselected areas.

After the powder sprayer unit is placed in operation, the powderdistribution is observed and the roller speed and blade pressure areadjusted until a desired dispensing rate is achieved. If the powderldistribution is uneven, las may be caused by inaccuracies in thedispensing roller or side panels or by uneven wear, this is easilycorrected iby adjusting the blade pressure in appropriate selectedareas. In cases where a particular uneven distribution is desired, forexample, more powder in the center than at the ends, such unevendistribution can be attained by adjusting the blade pressure so that itis greater at the ends than at the center.

The position of the ydischarge tubes can be adjusted so that one or bothof the tubes are effective, and hence, the effective strength of theelectrostatic iield can be varied over a relatively wide range. Also,the tube position can Ibe adjusted to provide an electrostatic fieldwhich is nonsymmetrical and which thus tends to propel powderparticlesin other than a directly downward direction. The non-symmetrical iieldcan be used, for example, to compensate for the effect of ambient aircurtains on the powder particles as they fall from the dispensing rollerto the surface below.

When the unit is placed in operation, a pneumatic pressure is created inthe plenum chambers by means of a suitable air pump to thereby create anair curtain on each side ofthe roller. These air curtains extend betweenthe side panels and the surface below and thereby protect the enclosedarea from ambient air currents.

Although only a few illustrative embodiments of the 10 invention havebeen described in detail, it should be obvious to persons skilled in theart that there are numerous additional variations and embodiments withinthe scope of this invention. This invention is more particularly definedin the appended claims.

What is claimed is:

1. In an electrostatic powder sprayer, the combination a pair of spacedapart end members;

means between said end members defining a receptacle for powder materialto be dispensed;

a cylindrical noller journaled between said end members within anopening below said receptacle;

wiping blade means secured to said receptacle and positioned to engagesaid roller for forming a dispensing mechanism for metering out powdermaterial from said receptacle at a substantially uniform rate;

means providing a like arcuate surface on each of said end members, saidarcuate surfaces being eccentric with respect to the cylindrical surfaceof said roller;

an elongated electrode means capable of providing an electrostaticfield;

a pair of spaced-apart socket members adapted to secure the ends of saidelongated electrode;

a pair of socket support members each adapted to slidably engage adifferent one of said arcuate surfaces, each of said socket membersbein-g secured to a different one of said support members so that saidtubular means is adjustable to various positions generally parallel tothe axis of said dispensin-g roller and in the .vicinity of said wipingblades; and

means for energizing said tubular means to create an electrostatic ieldto free powder material from said roller and to disperse the same sothat said powder can fall evenly to the surface below. y

2. Apparatus in accordance with claim 1 wherein said socket members arepivotably secure to said socket support members.-

3. Apparatus is accordance with claim 1 wherein said tubular means isdetachably secured between said pair of spaced-apart socket members.

References Cited by the Examiner UNITED STATES PATENTS 1,986,047 1/1935Dawley et al 118-3213 X 2,027,307 1/1936 Schacht 117-17 X 2,027,3081/1936 Schacht 117-17 X 2,394,657 2/ 1946 Beregh 95-1.7 X 2,972,332 2/1961 Limberger 95-1.7 X 3,114,482 12/ 1963 Dunaway 222-328 X 3,221,93812/1965 Yonkers et al 317-2 X MILTON O. HIRSHFIELD, Primary Examiner.MAX L. LEVY, SAMUEL BERNSTEIN, Examiners. I A. SILVERMAN, AssistantExaminer.

1. IN AN ELECTROSTATIC POWDER SPRAYER, THE COMBINATION OF A PAIR OFSPACED APART END MEMBERS; MEANS BETWEEN SAID END MEMBERS DEFINING ARECEPTACLE FOR POWDER MATERIAL TO BE DISPENSED; A CYLINDRICAL ROLLERJOURNALED BETWEEN SAID END MEMBERS WITHIN AN OPENING BELOW SAIDRECEPTACLE; WIPING BLADE MEANS SECURED TO SAID RECEPTACLE AND POSITIONEDTO ENGAGE SAID ROLLER FOR FORMING A DISPENSING MECHANISM FOR METERINGOUT POWDER MATERIAL FROM SAID RECEPTACLE AT A SUBSTANTIALLY UNIFORMRATE; MEANS PROVIDING A LIKE ARCUATE SURFACE OF EACH OF SAID ENDMEMBERS, SAID ARCUATE SURFACES BEING ECCENTRIC WITH RESPECT TO THECYLINDRICAL SURFACE OF SAID ROLLER; AN ELONGATED ELECTRODE MEANS CAPABLEOF PROVIDING AN ELECTROSTATIC FIELD; A PAIR OF SPACED-APART SOCKETMEMBERS ADAPTED TO SECURE THE ENDS OF SAID ELONGATED ELECTRODE; A PAIROF SOCKET SUPPORT MEMBERS EACH ADAPTED TO SLIDABLY ENGAGE A DIFFERENTONE OF SAID ARCUATE SURFACES, EACH OF SAID SOCKET MEMBERS BEING SECUREDTO A DIFFERENT ONE OF SAID SUPPORT MEMBERS SO THAT SAID TUBULAR MEANS ISADJUSTABLE TO VARIOUS POSITIONS GENERALLY PARALLEL TO THE AXIS OF SAIDDISPENSING ROLLER AND IN THE VICINITY OF SAID WIPING BLADES; AND MEANSFOR ENERGIZING SAID TUBULAR MEANS TO CREATE AN ELECTROSTATIC FIELD TOFREE POWDER MATERIAL FROM SAID ROLLER AND TO DISPERSE THE SAME SO THATSAID POWDER CAN FALL EVENLY TO THE SURFACE BELOW.